First principles calculations were done with the siesta [1]}, [2]} implementation of the density functional theory (DFT) method. We employed the local density approximation (LDA) exchange-correlation functional as parametrized J. P. Perdew and Y. Wang [3]} in conjunction with optimized norm-conserving Vanderbilt (ONCV) scalar-relativistic pseudopotentials [4]}, [5]} with \(2s\)  and \(2p\)  valence electrons. The Brillouin zone was sampled using a \(\Gamma \) -centered, one-dimensional grid with 78 k-points for the pristine armchair nanotubes.
